This invention relates to an optical glass having refractive indices (Nd) of about 1.71 to about 1.80 and Abbe values (.nu.d) of about 46 to about 38 and consisting basically of a B.sub.2 O.sub.3 -- SiO.sub.2 -- La.sub.2 O.sub.3 -- ZrO.sub.2 -- TiO.sub.2 -- ZnO -- BaO system.
Known in the art of the optical glass having the above described optical properties are ones consisting of a B.sub.2 O.sub.3 -- SiO.sub.2 -- La.sub.2 O.sub.3 -- ZrO.sub.2 -- TiO.sub.2 -- Ta.sub.2 O.sub.5 (and/or Nb.sub.2 O.sub.5 and/or WO.sub.3) -- divalent metal oxides system, as disclosed in U.S. Pat. No. 3,143,432, German Offenlegungsschrift No. 1,496,524 and Japanese Laid-open Publication Nos. 59116/1973, 88106/1973 and 101414/1975. These known optical glasses contain, as their essential ingredients, a B.sub.2 O.sub.3 -- SiO.sub.2 -- La.sub.2 O.sub.3 divalent metal oxides system and further contain ZrO.sub.2, TiO.sub.2 and a relatively large quantity of Ta.sub.2 O.sub.5 etc. which are added for preventing devitrification and achieving desired optical parameters. The optical glasses of this known system, however, are disadvantageous in that they require a relatively high temperature and a long time in melting and, besides, it is difficult to obtain a homogeneous optical glass which is substantially free of seeds.